1. Field of the Invention
The present invention relates to a positive resist composition suitable for use in the ultramicrolithography process such as production of VLSI or a high-capacity microchip or in other photofabrication processes, and a pattern forming method using the same. More specifically, the present invention relates to a positive resist composition capable of forming a high-resolution pattern by using electron beam, X-ray or EUV and a pattern forming method using the same. That is, the present invention relates to a positive resist composition suitably usable for fine processing of a semiconductor device, where electron beam, X-ray or EUV light is used, and a pattern forming method using the same.
2. Description of the Related Art
In the process of producing a semiconductor device such as IC and LSI, fine processing by lithography using a photoresist composition has been conventionally performed. Recently, the integration degree of an integrated circuit is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using electron beam, X ray or EUV is proceeding.
The lithography using electron beam or EUV is positioned as a next-generation or next-next-generation pattern formation technique, and development of a positive resist is proceeding.
In the actual field of semiconductor fine processing, the aging stability of the resist composition is a problem. Usually, in producing VLSI or a high-capacity microchip, there is employed a system of preparing and storing only a resist composition in a large amount and step-by-step using a necessary amount of the resist therefrom at the semiconductor fine processing. However, the conventional resist composition for electron beam or EUV undergoes a change in sensitivity with aging and this requires to vary the exposure amount, development conditions and the like between when using a resist immediately after preparation and when using a resist at a later time after the preparation, which hampers mass production.
With respect to such a positive resist, there are conventionally known some resist compositions using a phenolic acid-decomposable resin obtained by copolymerizing an acid-decomposable acrylate monomer having an alicyclic group as the acid-decomposable group. Examples thereof include positive resist compositions disclosed in U.S. Pat. No. 5,561,194, JP-A-2001-166474 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2001-166478, JP-A-2003-107708, JP-A-2001-194792 and JP-A-2005-234434. Also, a case using a compound capable of generating a sulfonic acid upon irradiation with an actinic ray or radiation and a compound capable of generating a carboxylic acid is disclosed in JP-A-2001-107707. Furthermore, a case using a photodecomposable base is disclosed in JP-A-6-242606, JP-A-2006-208781 and JP-A-2007-210904.
In these resist compositions using a low-molecular phenol compound as the main component, high dissolution contrast may be obtained but, on the other hand, there is a problem in the aging stability and the like.